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# Vertex normals calculation, any good?

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Hi all. After getting very usefull reaction on other threads, I'm wondering if I did will creating a new "Vertexnormal calculation"-function. What do you think?
void GLobject::CalcNormals()
{
int c, c2;

for(c=0;c<nr_vertices;c++)
{
normals[c].x = 0.0f;
normals[c].y = 0.0f;
normals[c].z = 0.0f;
}
for(c=0;c<nr_faces;c++)
{
facenormals[c] = GetFaceNormal(vertices[faces[c].v1],
vertices[faces[c].v2],
vertices[faces[c].v3]);
}

for(c=0;c<nr_vertices;c++)
{
for(c2=0;c2<nr_faces;c2++)
{
if(faces[c2].v1 == (unsigned int)c)
{
normals[faces[c2].v1].x += facenormals[c2].x;
normals[faces[c2].v1].y += facenormals[c2].y;
normals[faces[c2].v1].z += facenormals[c2].z;
}
if(faces[c2].v2 == (unsigned int)c)
{
normals[faces[c2].v2].x += facenormals[c2].x;
normals[faces[c2].v2].y += facenormals[c2].y;
normals[faces[c2].v2].z += facenormals[c2].z;
}
if(faces[c2].v3 == (unsigned int)c)
{
normals[faces[c2].v3].x += facenormals[c2].x;
normals[faces[c2].v3].y += facenormals[c2].y;
normals[faces[c2].v3].z += facenormals[c2].z;
}
}
}

for(c=0;c<nr_vertices;c++)
{
normals[c] = Normalize(normals[c]);
}
}



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If you're just averaging the normals from the faces it's not always gonna look good. For example if you have a cube with only 1 normal per-vertex, it's gonna look quite funky.

You should average the normals unless the angle between them
is too great.

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Well your function is quite inefficient. For one thing you shouldn't use a loop to fill an array with initial values. Use a memory setting function like memset. Also the copy of your face normals is not necessary. It's just "spinning your CPU's wheels" for no good reason. Instead, do something like this:

void MakeVertexNormals( void ){    int shared = 0;    vector_t sum = { 0, 0, 0 };    const vector_t zero = { 0, 0, 0 };    for( int i = 0; i < num_verts; ++i )    {         for( int j = 0; j < num_faces; ++j )         {              if( model->faces[j].vertexIndex[0] == i ||                  model->faces[j].vertexIndex[1] == i ||                  model->faces[j].vertexIndex[2] == i )              {                  sum = VectorAdd( sum, &GetFaceNormal( j ) );                  ++shared;              }         }         // divide sum by shared and normalize         model->normals = Norm( VectorDivide( sum, shared ) );         sum = zero;         shared = 0;    }}

-SirKnight

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Thanks for the explanation sir knight.
It sounds logic that I don't need an array for all facenormals, because I don't use them anywhere else in the engine (yet).

Thanks.
I've changed the function to this, according to your exaplanation:
void GLobject::CalcNormals(){	int c, c2, shared = 0;	Vertex facenormal = SetVector(0, 0, 0);	Vertex sum = SetVector(0, 0, 0);	for(c=0;c<nr_vertices;c++)	{		for(c2=0;c2<nr_faces;c2++)		{			if(faces[c2].v1 == (unsigned int)c || 			   faces[c2].v2 == (unsigned int)c || 			   faces[c2].v3 == (unsigned int)c)			{				facenormal = GetFaceNormal(vertices[faces[c2].v1],				   						   vertices[faces[c2].v2],										   vertices[faces[c2].v3]);				shared++;				sum = AddVector(sum, facenormal);			}		}		sum = DivideVector(sum, (float)shared);		normals[c] = Overtake(sum);		Normalize(normals[c]);		sum = SetVector(0, 0, 0);		shared = 0;	}}

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Also you're for each vertex looping over all the faces. You should loop twice over all the vertices, and once over all the faces, like this:

int c;

for (c=0;c normals[c]=Vector(0,0,0);
}

for (c=0;c Vector normal=GetFaceNormal(c);

normals[faces[c].v1]+=normal;
normals[faces[c].v2]+=normal;
normals[faces[c].v3]+=normal;
}

for (c=0;c normals[c].normalize();
}

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Ooops, that message didn't come out right. First loop is over all vertices, second over all faces, and third over all vertices again (just to normalize them).

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